Tutorial.Stopwatch History

A sketch that demonstrates how to do two (or more) things at once by using millis().

/* StopWatch
* Paul Badger 2008
* Demonstrates using millis(), pullup resistors,
* making two things happen at once, printing fractions
*
* Physical setup: momentary switch connected to pin 4, other side connected to ground
* LED with series resistor between pin 13 and ground
*/
#define ledPin 13 // LED connected to digital pin 13
#define buttonPin 4 // button on pin 4
int value = LOW; // previous value of the LED
int buttonState; // variable to store button state
int lastButtonState; // variable to store last button state
int blinking; // condition for blinking - timer is timing
long interval = 100; // blink interval - change to suit
long previousMillis = 0; // variable to store last time LED was updated
long startTime ; // start time for stop watch
long elapsedTime ; // elapsed time for stop watch
int fractional; // variable used to store fractional part of time
void setup()
{
Serial.begin(9600);
pinMode(ledPin, OUTPUT); // sets the digital pin as output
pinMode(buttonPin, INPUT); // not really necessary, pins default to INPUT anyway
digitalWrite(buttonPin, HIGH); // turn on pullup resistors. Wire button so that press shorts pin to ground.
}
void loop()
{
// check for button press
buttonState = digitalRead(buttonPin); // read the button state and store
if (buttonState == LOW && lastButtonState == HIGH && blinking == false){ // check for a high to low transition
// if true then found a new button press while clock is not running - start the clock
startTime = millis(); // store the start time
blinking = true; // turn on blinking while timing
delay(5); // short delay to debounce switch
lastButtonState = buttonState; // store buttonState in lastButtonState, to compare next time
}
else if (buttonState == LOW && lastButtonState == HIGH && blinking == true){ // check for a high to low transition
// if true then found a new button press while clock is running - stop the clock and report
elapsedTime = millis() - startTime; // store elapsed time
blinking = false; // turn off blinking, all done timing
lastButtonState = buttonState; // store buttonState in lastButtonState, to compare next time
// routine to report elapsed time
Serial.print( (int)(elapsedTime / 1000L)); // divide by 1000 to convert to seconds - then cast to an int to print
Serial.print("."); // print decimal point
// use modulo operator to get fractional part of time
fractional = (int)(elapsedTime % 1000L);
// pad in leading zeros - wouldn't it be nice if
// Arduino language had a flag for this? :)
if (fractional == 0){
Serial.print("000"); // add three zero's
else if (fractional < 10) // if fractional < 10 the 0 is ignored giving a wrong time, so add the zeros
Serial.print("00"); // add two zeros
else if (fractional < 100)
Serial.print("0"); // add one zero
}
Serial.println(fractional); // print fractional part of time
}
else{
lastButtonState = buttonState; // store buttonState in lastButtonState, to compare next time
}
// blink routine - blink the LED while timing
// check to see if it's time to blink the LED; that is, the difference
// between the current time and last time we blinked the LED is larger than
// the interval at which we want to blink the LED.
if ( (millis() - previousMillis > interval) ) {
if (blinking == true){
previousMillis = millis(); // remember the last time we blinked the LED
// if the LED is off turn it on and vice-versa.
if (value == LOW)
value = HIGH;
else
value = LOW;
digitalWrite(ledPin, value);
}
else{
digitalWrite(ledPin, LOW); // turn off LED when not blinking
}
}
}

fractional = (int)(elapsedTime % 1000L);
if (fractional < 100) // if fractional < 100 the 0 is ignored giving a wrong time, so add the zero
Serial.print("0"); // add zero
if (fractional < 10){
Serial.print("0"); // and another one
else if (fractional == 0)
Serial.print("00"); // and two for three total

to:

fractional = (int)(elapsedTime % 1000L);
// padd in leading zeros - wouldn't it be nice if
// Arduino language had a flag for this :)
if (fractional == 0){
Serial.print("000"); // add three zero's

else if (fractional < 10) // if fractional < 10 the 0 is ignored giving a wrong time, so add the zeros
Serial.print("00"); // add zero
else if (fractional < 100)
Serial.print("0"); // add another one

Serial.print("0"); // add zero
if (fractional < 10)
Serial.print("0"); // and another one
else if (fractional == 0)
Serial.print("00"); // and two for three total

}

to:

// use modulo operator to get fractional part of time
fractional = (int)(elapsedTime % 1000L);
if (fractional < 100) // if fractional < 100 the 0 is ignored giving a wrong time, so add the zero
Serial.print("0"); // add zero
if (fractional < 10){
Serial.print("0"); // and another one
else if (fractional == 0)
Serial.print("00"); // and two for three total
}

Stopwatch

A sketch that demonstrates how to do two (or more) things at once by using millis().

/* StopWatch
* Paul Badger 2008
* Demonstrates using millis(), pullup resistors, making two things happen at once, printing fractions
*
* Physical setup: momentary switch connected to pin 4, other side connected to ground
* LED with series resistor between pin 13 and ground
*/
#define ledPin 13 // LED connected to digital pin 13
#define buttonPin 4 // button on pin 4
int value = LOW; // previous value of the LED
int buttonState; // variable to store button state
int lastButtonState; // variable to store last button state
int blinking; // condition for blinking - timer is timing
long interval = 100; // blink interval - change to suit
long previousMillis = 0; // variable to store last time LED was updated
long startTime ; // start time for stop watch
long elapsedTime ; // elapsed time for stop watch
int fractional; // variable used to store fractional part of time
void setup()
{
Serial.begin(9600);
pinMode(ledPin, OUTPUT); // sets the digital pin as output
pinMode(buttonPin, INPUT); // not really necessary, pins default to INPUT anyway
digitalWrite(buttonPin, HIGH); // turn on pullup resistors. Wire button so that press shorts pin to ground.
}
void loop()
{
// here is where you'd put code that needs to be running all the time.
// check for button press
buttonState = digitalRead(buttonPin); // read the button state and store
if (buttonState == LOW && lastButtonState == HIGH && blinking == false){ // check for a high to low transition
// if true then found a new button press while clock is not running - start the clock
startTime = millis(); // store the start time
blinking = true; // turn on blinking while timing
delay(5); // short delay to debounce switch
lastButtonState = buttonState; // store buttonState in lastButtonState, to compare next time
}
else if (buttonState == LOW && lastButtonState == HIGH && blinking == true){ // check for a high to low transition
// if true then found a new button press while clock is running - stop the clock and report
elapsedTime = (millis() - startTime) - 5; // store elapsed time (-5 to make up for switch debounce time)
blinking = false; // turn off blinking, all done timing
lastButtonState = buttonState; // store buttonState in lastButtonState, to compare next time
// routine to report elapsed time
Serial.print( (int)(elapsedTime / 1000L) ); // divide by 1000 to convert to seconds - then cast to an int to print
Serial.print("."); // print decimal point
fractional = (int)(elapsedTime % 1000L); // use modulo operator to get fractional part of time
Serial.println(fractional); // print fractional part of time
}
else{
lastButtonState = buttonState; // store buttonState in lastButtonState, to compare next time
}
// blink routine - blink the LED while timing
// check to see if it's time to blink the LED; that is, is the difference
// between the current time and last time we blinked the LED bigger than
// the interval at which we want to blink the LED.
if ( (millis() - previousMillis > interval) ) {
if (blinking == true){
previousMillis = millis(); // remember the last time we blinked the LED
// if the LED is off turn it on and vice-versa.
if (value == LOW)
value = HIGH;
else
value = LOW;
digitalWrite(ledPin, value);
}
else{
digitalWrite(ledPin, LOW); // turn off LED when not blinking
}
}
}